1. Field of the Invention
This invention relates generally to fillers for thermoplastic polymeric systems. More particularly, this invention relates to a modified filler based on a mica-like mineral sheet silicate.
2. The Prior Art
Thermoplastic polymers are finding an increasing number of uses, especially as structural materials. These thermoplastic polymers are especially attractive as replacements for metals because of the reduction in weight that can often be achieved, as for example, in automotive applications. However, for a particular application, the thermoplastic polymer by itself may not offer the combination of properties desired and, therefore means to correct this deficiency are of interest. In order to increase the rigidity and strength of thermoplastic polymers, it is a common practice to incorporate a quantity of filler, natural or synthetic, in the form of fibers or flakes. When the mixture of polymer and flakes is injection molded into a sheet form, the flow causes the particles of filler to line up parallel to the sheet. If the particles have a high aspect ratio and have a high rigidity and strength, they will then constitute an effective reinforcement in the direction of alignment. Nevertheless, some flakes will become bent during the molding process. However, if the flakes are very strong, then the original aspect ratio will be retained. Further, in most cases the surfaces of the flakes are not coupled, i.e., chemically cross-linked to the polymer, and the bond may be weak.
There are important filler/polymer combinations where no practical means is available to affect a graft at the interface, e.g., a polypropylene/mica flake blend. In such a case a new approach is needed, especially to improve the mechanical properties of the filled polymer system. The present invention constitutes a new method resulting in a significant improvement in the reinforcement efficiency irrespective of whether or not a coupling agent is incorporated into the composite.